SUMMARY Household air pollution (HAP) causes significant health and economic effects in low and middle-income countries (LMICs). Chronic exposure to HAP has been associated with decline in lung function and subsequent development of chronic obstructive pulmonary disease (COPD). Due to the burden of HAP and subsequent risk of developing COPD, quality of life of those exposed has resulted in 81.1 million disability-adjusted life years (DALYs) lost annually, just over 3% of all DALYs experienced worldwide. Attention has recently shifted focus from more efficient biomass burning stoves to using clean burning fuels, such as liquefied petroleum gas (LPG), to lower HAP because the former has failed to reduce exposure levels to international safety standards in multiple randomized trials. While there is evidence for using LPG to prevent disease, there is little knowledge about whether use of clean fuels is actually a cost-effective strategy to improve health outcomes. We hypothesize an LPG stove and fuel distribution program will be a cost-effective mechanism to lower HAP and improve participants' quality of life and decrease the rate of lung function decline. To make this evaluation, we propose performing a cost-effectiveness evaluation to the already existing trial, the Cardiopulmonary outcomes and Household Air Pollution (CHAP). This proposal will use cost, spirometry, and quality of life data collected as part of the parent trial to make this assessment. Our primary outcome will be the incremental cost effectiveness ratio (ICER), expressed in 2018 USD per quality-adjusted life year (QALY) gained, comparing LPG stoves and fuel distribution to the current standard of care. This proposal has two novel aims. First, we will estimate the ICER of an LPG stove and fuel distribution intervention relative to standard of care from baseline to the end of the intervention (1 year). The ICER will be calculated by comparing the difference in total costs and total QALYs between the intervention and controls over the 1-year intervention period. Second, we will predict the cost-effectiveness of LPG stoves and fuel distribution if continued over the lifetime of intervention participants vs. control participants. A markov (state- transition) model will be built to predict the natural history of lung function decline and will determine total costs and QALYs over the course of a participants' lifetime to determine the ICER. Economic evaluations are critical extensions of randomized controlled trials in that they expand the evidence base from a narrow evaluation of intervention efficiency to a broader understanding of whether scaling up interventions would likely provide good value for the money. A cost effectiveness evaluation provides guidance on using scarce resources to have the greatest possible impact on health. Results from this study will inform public health interventions aimed at reducing HAP and the burden of disease globally.